feet

Ladder drills are excellent! Get a rope ladder, they usually come with drills or you can look them up online.

Dot drills.  

He can do them on any floor with square tiles.  Google the phrase and you'll find lots of variations and sequences.  Pick a routine he can do in about 2 minutes or less that makes him go forward/backward and turn both ways on both one and two feet.  Do the routine 5-10 times every day just in the course of going about his daily business.  Within a month, he'll cut his dot drill time in half, and the quickness will be apparent on the field.

Foot quickness is something you can improve quickly.

Best wishes,

Jump rope.

The drills mentioned are always good to increase quickness of the feet and the mind.

You may consider the following for immediate success.

1. Play deeper at 3b and take a few steps toward the batter on each pitch.

2. Watch the on deck hitter, learn to "read the bat". Know your pitcher.

3. Study U-tube of the great ML 3b - Nettles, Robinson, Rosen, Schmidt.

4. Be light on your feet, move your "puppies".

Good Luck;

Bob

He is in college so get with the strength and conditioning coach and get a more specific workout workout designed for sprinters.

D'oh go out and sprint. Every three days change up and do "unders" and "overs" 10x per day. Sprint 20 yds one day 40-60 another and 100yds another. On the short days focus on technique out of the box, on the overs (100) focus on getting through the full 100 at full speed. If he can find a sprint coach they will have bands for doing short 20yd sprints out of the box. He will need to recover so don't attempt every day go every three days. 

Speed can be improved but it takes a long time.